The invention claimed and disclosed herein pertains to imaging devices and more particularly, to optimizing color plane registration for imaging devices.
Various types of imaging devices are known in the art. The term xe2x80x9cimaging devicexe2x80x9d as used herein refers to any device that is configured to produce a visual image on an image media. Imaging devices include devices commonly known as printers, copiers, facsimile machines, and the like. Image media includes paper and plastic sheet material. Generally, imaging devices employ various techniques to deposit ink or powdered toner onto an image media to produce an image-product. The term xe2x80x9cimage-productxe2x80x9d as used herein denotes a piece of image media that bears at least one image thereon.
Imaging devices that are configured to produce multi-colored images are also known in the art. The term xe2x80x9cmulti-colored imagexe2x80x9d means an image that comprises more than one color, wherein one of the xe2x80x9ccolorsxe2x80x9d can be black. Various types of printed graphics as well as photo-quality images can be produced on prior art imaging devices. Such prior art imaging devices are also generally capable of producing monochromatic images. For example, many prior art imaging devices, in addition to having the capability to produce multi-colored images, are also capable of producing images in the form of monochromatic text comprising black alpha-numeric characters on white image media.
Of the various types of prior art imaging devices in use, one of the more popular types is that commonly known as the xe2x80x9claser printer.xe2x80x9d It is understood that the xe2x80x9claser printerxe2x80x9d is used for most types of image devices including copiers and facsimile machines in addition to printers. Thus, the term xe2x80x9claser printerxe2x80x9d is generally used within the art to denote any imaging device that employs the laser scanning process for producing image-products. Laser printers are available with multi-color capability, although many laser printers have only monochromatic capability.
Laser printers having multi-color capability generally employ four xe2x80x9ccolorsxe2x80x9d of toner to produce images that can comprise a substantially full color gamut. Such imaging devices are often referred to as xe2x80x9cfour-color laser printers.xe2x80x9d The four colors of toner generally utilized are those of black, cyan, magenta, and yellow. Known techniques of applying various combinations of the four different toners can yield a wide array of colors in an image-product.
Laser scanning imaging devices (xe2x80x9claser printersxe2x80x9d) generally employ at least one beam of light which is commonly a laser beam. The beam is scanned laterally across a moving, electrostatically charged, photosensitive surface in order to xe2x80x9cexposexe2x80x9d selected portions of the surface in accordance with a particular image to be produced. That is, the beam generally scans a latent image-into the photo-sensitive surface, wherein the latent image is characterized by a difference in electrical potential relative to portions of the surface that do not form the image. Powdered toner is then applied to the latent image which results in an image formed from toner. That is, the toner is attracted to the latent image and is not attracted to portions of the photo-sensitive surface that are not part of the latent image. The toner image is then ultimately transferred to an image media such as a sheet of paper or the like.
In a four-color laser printing process, the above-described process of forming an image from toner is performed separately for each of the colors of toner used to thereby produce the overall image. Each of these images comprising a single toner is referred to as a xe2x80x9ccolor plane.xe2x80x9d The overall image comprises all of the color planes together (i.e., all of the color planes used for the overall image, which can be one, two, three or four of the colors). Generally, each of the color planes is formed separately in this manner and then all the color planes are brought together to form the overall image. There are several known methods of forming the color planes to make up an overall image. Two of these methods are known respectively as xe2x80x9csingle-passxe2x80x9d and xe2x80x9cfour-passxe2x80x9d color imaging.
Turning now to FIG. 1, a side-elevation schematic diagram is shown which depicts some of the major components of a typical prior art single-pass, four-color laser imaging device (xe2x80x9cprinterxe2x80x9d) 10. As is seen, the prior art printer 10 comprises a plurality of electro-statically chargeable photosensitive surfaces (xe2x80x9cphotoconductorsxe2x80x9d) 11 that are substantially in the form of cylindrical drums. Each of the photoconductors 11 is configured to rotate in a process direction indicated by the respective arrow, as marked. The prior art printer 10 also comprises a plurality of laser devices 13. Each one of the laser devices 13 corresponds to a respective photoconductor 11 as shown. Further, each of the laser devices 13 is configured to generate a laser beam xe2x80x9cLB.xe2x80x9d The laser beam xe2x80x9cLBxe2x80x9d is selectively pulsed and is laterally scanned across the respective photoconductor 11 in a scan direction (not shown) as the photoconductor rotates. The scan direction is generally substantially perpendicular to the process direction. As a result of the scanning laser, the respective latent color plane is generated on the surface of each photoconductor 11, as explained above.
In addition to the laser devices 13, several toner hoppers 15 are included in the prior art printer 10. As is seen, each one of the toner hoppers 15 corresponds to a respective photoconductor 11. Each of the toner hoppers 15 are configured to deposit, on the respective photoconductor 11, one of the toners of which there are four colors as explained above. Thus, each of the four color planes which can make up a given image is produced on a respective photoconductor 11 by way of the corresponding laser device 13 and toner hopper 15.
The prior art printer 10 typically also includes a controller 20 as shown. The controller 20 is generally linked in signal communication with each of the laser devices 11. The controller 20 can be linked with other components of the printer 10 as well. The controller 20 is configured to control the selective pulsing and scanning of the laser devices 11 so as to generate the latent color plane on each respective photoconductor. The controller 20 can also be configured to control various other operational aspects of the printer 10 as will be explained below. The prior art printer 10 can comprise a sensor 21 which is linked in signal communication with the controller 20. The operation of the sensor 21 will be explained below.
As revealed in FIG. 1, a print path xe2x80x9cPPxe2x80x9d is defined by the printer 10. The print path xe2x80x9cPPxe2x80x9d is generally defined by various media-handling components such as feed rollers (not shown), media guides (not shown), and the like. The print path xe2x80x9cPPxe2x80x9d is configured to convey there along an image media xe2x80x9cM,xe2x80x9d such as a sheet of paper, in the direction indicated by the arrow 30. As the media xe2x80x9cMxe2x80x9d is conveyed along the print path xe2x80x9cPP,xe2x80x9d each of the color planes that are to be produced on the respective photoconductors 11 is successively transferred there from, one on top of the other, to the media xe2x80x9cM.xe2x80x9d Thus, by the time the media xe2x80x9cMxe2x80x9d passes the sensor 21, all of the color planes have been generated and transferred to the media, to form the overall image thereon. It should be observed that an overall image does not need to be formed from all of the available colors, and can be formed from individual colors or any combination thereof.
Because all four of the color planes together can form the overall image, the quality of the overall image is dependent upon the alignment of each of the color planes relative to one another. That is, in order to produce a perfect overall image, the four color planes are preferably superimposed upon one another in perfect alignment as defined by the alignment of colors in the image source (i.e., a data file representative of the image, or an original document which is optically scanned to read an image thereon). An image having misaligned color planes can appear to lack sufficient sharpness and clarity and/or can appear somewhat disjointed. The concept of alignment of the color planes which make up an image is known as xe2x80x9ccolor plane registrationxe2x80x9d (CPR). The color plane registration of a given image can depend upon many factors. Among these factors are the timing and coordination of each of the laser devices 13 as well as the timing and coordination of each of the photoconductors 11.
Generally, the timing and coordination of the laser devices 13 and photoconductors 11 can be controlled by way of the controller 20 and the sensor 21. As mentioned above, the sensor 21 is linked in signal communication with the controller 20. The sensor is configured to detect irregular color plane registration and to notify the controller 20 of such irregularities. The controller 20 can then make corrective adjustments as required with respect to the control of the laser devices 13 and photoconductors 11. This process is preferably performed using a predefined calibration image which can be stored as a digital data file in the imaging device and retrieved to generate a printed calibration image. The resultant printed calibration image can then be compared against the calibration image data file using sensors, and any differences between the printed image and the calibration file can be detected. The imaging device can then be adjusted so that the printed calibration image more closely resembles the calibration ideal image as represented by the calibration data file.
For example, the printer 10 can be configured to periodically print a test calibration image (not shown). When the test calibration image is printed, the sensor 21 can detect any irregularities in the color plane registration of the calibration image. The sensor 21 then sends a signal to the controller 20, wherein the signal contains data indicative of the nature and extent of the irregularities, for example. The controller 20 can then receive the signal and evaluate the data to determine what corrective adjustments are needed to optimize the color plane registration.
Examples of such adjustments can include, by way of example only, alignment of the lasers or the laser beams using adjustable optics, timing of the lasers (both rate of scan and time to begin initial scan), the rotational speed of the photoconductor on which a single color image is scanned by the laser, the physical alignment of the photoconductors with respect to one another, and with respect to a media path or an intermediate transfer medium disposed between the photoconductors and the media, and the rate of travel of any such intermediate transfer medium. Methods and apparatus for adjusting each of these parameters, as well as other parameters which can affect color plane registration, are well known in the art.
However, several causes of irregular color plane registration exist which cannot be totally corrected by way of the procedure explained above. For example, differences in the size and shape of the photoconductors 11 relative to one another can cause uncorrectable irregularities in color plane registration. Such differences in the size and shape of the photoconductors 11 are most often caused by standard manufacturing tolerances and the like. That is, the photoconductors 11 can be economically manufactured only to within given dimensional tolerances. This, in turn, inevitably results in slight variations in size and shape of the photoconductors 11 relative to one another. As a result, slight variations in alignment between the respective color planes can occur as the color planes are transferred from the photoconductors 11 to the media xe2x80x9cM.xe2x80x9d
The controller 20, along with the sensor 21, can compensate for such irregularities in color plane registration which are caused by manufacturing tolerances and the like. However, these irregularities cannot be totally eliminated from the final image-product by the compensation process described above with respect to the controller 20 and the sensor 21. A typical prior art remedy for the irregularities in color plane registration which result from manufacturing tolerances and the like is to minimize the irregularities as an average over the entire sheet of media xe2x80x9cM.xe2x80x9d That is, prior art printers 10 are typically configured to detect color plane registration irregularities by way of the sensor 21, for example, and then compute a corrective adjustment solution which will result in an average optimization of the image over substantially the entire page with respect to the color plane registration.
The means of compensating for color plane registration irregularities and for creating an average solution over the entire page is well understood in the art. Such means can include adjusting the timing, movement, alignment, and the like, of the laser devices 13 as well as of the photoconductors 11, as explained above. Because the prior art solution for dealing with irregularities in color plane registration results in only an average solution, prior art printers 10 can prove unsatisfactory for users who require a sharp, clear multi-color image in a predetermined region of the sheet of media xe2x80x9cM.xe2x80x9d Furthermore, the sensor 21 is typically configured to detect color plane registration irregularities on only a portion of the sheet of media xe2x80x9cM.xe2x80x9d For example, prior art printers 10 typically include sensors 21 that are configured to monitor only an edge of the image area of a sheet of media xe2x80x9cM.xe2x80x9d Alternatively, the prior art sensor 21 is configured to monitor only the center of the sheet of media xe2x80x9cM.xe2x80x9d Thus, the prior art provides limited means of correcting for irregularities in color plane registration, which means can prove unsatisfactory for many uses of the prior art printer 10. What is needed then are means for optimizing color plane registration in accordance with user demands, wherein such means achieve the benefits to be derived from similar prior art means, but which avoid the shortcomings and detriments individually associated therewith.
In accordance with one embodiment of the instant invention, a method of optimizing color plane registration includes focusing the color plane registration on a high-value zone. A high-value zone is an area of an image-page which contains at least a portion of a multicolor image for which image sharpness and clarity, and thus optimized color plane registration, is important. Thus, focusing the color plane registration means optimizing the color plane registration in a given region, or area, of a page of media, wherein the given region or area contains an image or a portion of an image for which optimization of color plane registration is desired. In accordance with another embodiment of the instant invention, a method of optimizing color plane registration includes minimizing color plane misalignment in a high value zone, wherein the high value zone can be defined by a user.
In accordance with yet another embodiment of the instant invention, a method of producing an image includes producing an image-page that has at least one multicolor image. The image-page (i.e., a sheet of media and including at least one image printed thereon) is displayed as well, which can include printing the image-page on a sheet of media, or displaying the image-page on a display screen such as a monitor or the like. A plurality of zones are defined on the image-page in order to assist in identifying the location of the high-value zone relative to the image-page. That is, a high-value zone is identified, wherein the color plane registration is to be optimized. That is, the color plane registration can then be optimized for the high-value zone by ensuring that color plane misalignment is minimized therein.
In accordance with still another embodiment of the instant invention, an imaging apparatus includes a print path that is configured to convey a sheet of media. A plurality of photoconductors is oriented relative to the print path so that each of the photoconductors can successively and ultimately deposit a respective color plane onto the sheet of media as the media moves along the print path and past the photoconductors. The color planes together with the sheet of media combine to form an image-product. At least one laser device is included in the apparatus. Each laser device can generate a latent color plane on a respective corresponding photoconductor. A controller is linked in signal communication with each of the laser devices and is configured to cause the laser devices to focus the color plane registration within the high-value zone.